1. Field of the Invention
The present invention relates to a rare earth magnet and a method for manufacturing the same.
2. Discussion of Related Art
Conventionally, in the manufacture of Rxe2x80x94Fexe2x80x94B rare earth sintered magnets, it has been proposed to add Niobium (Nb) to an alloy material for the purpose of obtaining finer crystal grains in the sintered bodies and improving the heat resistance of the magnets. Nb is known to suppress crystal grains from becoming coarse during sintering and to improve the magnetization properties of the magnet.
Japanese Laid-Open Patent Publication No. 7-94311 discloses a technique for improving the magnetic properties and the heat resistance of Ndxe2x80x94Fexe2x80x94Coxe2x80x94B sintered magnets by adding 0.1 to 2.0 wt % of Nb.
Japanese Patent Publication for Opposition No. 6-69003 discloses that the magnetic properties such as coercive force can be improved by adding 1 to 10 atom % (atomic percentage) of a metal element, for example Ti, Zr, Hf, Nb, in the production of rare earth magnet alloys by a quenching method.
The above conventional techniques have the following problems. In the technique disclosed in Japanese Laid-Open Patent Publication No. 7-94311, the alloy is produced by ingot casting. Therefore, the cooling rate of the alloy melt is low. At such a low cooling rate, a nonmagnetic boride such as NbFeB2 tends to be produced in a coarse grain state. If such coarse nonmagnetic boride is produced, the resultant rare earth magnet is hardened after sintering. This greatly deteriorates the efficiency of subsequent machining of the magnet, such as by cutting and surface polishing.
In the technique disclosed in Japanese Patent Publication for Opposition No. 6-69003, a large amount of the Nb metal, is added which also results in a nonmagnetic boride, such as NbFeB2, being produced. As a result, the remanence or residual flux density Br of the rare earth magnet decreases after sintering, and the processing efficiency of the magnet deteriorates.
A main object of the present invention is to provide a rare earth magnet superior in terms of both permanent magnetic properties and processability, and to provide a method for manufacturing such a rare earth magnet.
The rapidly solidified alloy of the present invention has a general formula represented by (Fe1-mTm)100-x-y-zQxRyMz where T denotes at least one element selected from the group consisting of Co and Ni, Q denotes at least one element selected from the group consisting of B and C, R denotes at least one rare earth element, and M denotes at least one kind of element selected from the group consisting of Nb and Mo, and the mole fractions x, y, z, and m respectively satisfy 2xe2x89xa6xxe2x89xa628 (atom %), 8xe2x89xa6yxe2x89xa630 (atom %), 0.1xe2x89xa6z less than 1.0 (atom %), and 0xe2x89xa6mxe2x89xa60.5 (atom %).
Preferably, the cooling rate at which the alloy material melt is quenched is in the range of 102 K/sec to 104 K/sec in order to rapidly solidify the alloy.
In a preferred embodiment, Niobium is present as an essential element.
In another preferred embodiment, the alloy includes an R2F14B compound in which the crystal grains have a minor-axis size in a range between 0.1 xcexcm and 100 xcexcm, a major-axis size in a range between 5 xcexcm and 500 xcexcm; and an R-rich phase dispersed at the grain boundaries of the crystal grains, the alloy has a thickness in a range between 0.03 mm and 10 mm.
The rare earth magnet of the present invention is then manufactured from any of the rapidly solidified alloys described above.
Additionally, the rare earth magnet of the present invention is manufactured from a rapidly solidified alloy to which Nb and/or Mo have been added in an amount in a range between 0.1 atom % and 1.0 atom %.
The method for manufacturing a rare earth magnet of the present invention includes the steps of:
producing a rapidly solidified alloy by quenching and solidifying a melt of an alloy having a general formula represented by (Fe1-mTm)100-x-y-zQxRyMz where T denotes at least one kind of element selected from the group consisting of Co and Ni, Q denotes at least one kind of element selected from the group consisting of B and C, R denotes at least one kind of rare earth element, and M denotes at least one kind of element selected from the group consisting of Nb and Mo, and the mole fractions x, y, z, and the mole fractions x, y, z, and m respectively satisfy 2xe2x89xa6xxe2x89xa628 (atom %), 8xe2x89xa6yxe2x89xa630 (atom %), 0.1xe2x89xa6z less than 1.0 (atom %), and 0xe2x89xa6mxe2x89xa60.5 (atom %); and
manufacturing a permanent magnet from the rapidly solidified alloy.
Preferably, in the step of producing a rapidly solidified alloy, the cooling rate is in a range between 102 K/sec to 104 K/sec.
In another preferred embodiment, the step of producing a rapidly solidified alloy is performed by strip casting a melt of the alloy.
In still another preferred embodiment, the method further includes the step of embrittling the rapidly solidified alloy by allowing the rapidly solidified alloy to occlude hydrogen and then release the hydrogen.